Transparent printed circuits are fabricated from transparent conductive sheets, which have a transparent base material and a transparent conductive layer formed on the transparent base material, through some processes such as etching or otherwise processing the transparent conductive layer into a desired pattern to form a transparent conductive pattern.
Existing general transparent touch panels are mainly fabricated with ITO (Indium Tin Oxide) transparent conductive sheets having an ITO thin film layer formed on the surface of a transparent base material (see Patent Literature 1).
More specifically, the ITO transparent conductive sheets have an ITO thin film layer formed on a sheet-like or film-like transparent base material, the transparent base material being made of glass or plastic such as polyethylene terephthalate (PET) by sputtering. The ITO thin film layer is etched or otherwise processed into a specified pattern so that a transparent conductive pattern is obtained.
However, due to recent diffusion of smart phones with a built-in transparent touch panel, the demand for the transparent touch panels made of ITO is growing. This makes it difficult to procure ITO transparent conductive sheets.
Moreover, the ITO transparent conductive sheets are costly in terms not only of the material, or ITO, itself, but also of production efficiency because the ITO thin film layer is formed by a sputtering technique. Further, another problem is that since the ITO thin film layer does not have flexibility, it is difficult to process the ITO transparent conductive sheets in a Roll to Roll process. Furthermore, yet another problem is that the transparent printed circuits produced from the ITO transparent conductive sheets cannot withstand a bending process involving small inflection encountered in the stage where the printed circuits are incorporated in or mounted on electronic equipment such as smart phones.
Transparent conductive sheets which can potentially solve the above problems (hereinafter referred to as “conductive polymer-based transparent conductive sheets”) are known which have a transparent conductive layer containing an organic transparent conductive polymer (polyethylene dioxythiophene (PEDOT) and the like) formed on the surface of a transparent base material (see Patent Literature 2).
There are also known nanowire-based transparent conductive sheets which have a transparent conductive layer containing a metal nanowire formed thereon (see Patent Literature 3). The transparent conductive layer of the nanowire-based transparent conductive sheets is made of a nanowire-containing transparent conductive material, which is prepared by, for example, dispersing and blending metal (Ag and the like) nanowires (or carbon nanotubes) into an organic resin matrix component. The nanowire-containing transparent conductive material is applied to a transparent base material and dried thereon to form the transparent conductive layer. In this case, the transparent base material is a plastic sheet/film made of polyester, polycarbonate or the like.
There are also known transparent conductive sheets having a combination of the conductive polymer-based transparent conductive sheets and the nanowire-based transparent conductive sheets, i.e., hybrid transparent conductive sheets having a transparent conductive layer formed with a transparent conductive material, which is prepared by dispersing and blending conductive nanowires into an organic transparent conductive polymer (see Patent Literature 4).
The aforementioned conductive polymer-based transparent conductive sheets, nanowire-based transparent conductive sheets, and hybrid transparent conductive sheets are given a generic name of “amorphous transparent conductive sheets.”
The amorphous transparent conductive sheets have a transparent conductive layer made of a transparent conductive material containing an organic transparent conductive polymer and/or conductive nanowires. The transparent conductive material is applied onto a transparent base material (PET film and the like) by bar coating or the like and dried thereon to form the transparent conductive layer.
Since the amorphous transparent conductive sheets can be manufactured through dispersing process, applying process, and drying process, the manufacturing cost thereof is lower than that of the ITO transparent conductive sheets which have an ITO thin film layer formed by the sputtering technique. The transparent conductive layer of the amorphous transparent conductive sheets also has an advantage of being flexible. Accordingly, the amorphous transparent conductive sheets are expected to find an application in substrates of optical devices and transparent flexible printed circuits (transparent FPCs).